The present invention relates to magnetic read and write heads and particularly to a combined magnetic write and read head for a recording medium wherein the medium is provided with at least one magnetizable storage layer which contains a magnetically anisotropic material, of which the axis of easy magnetization is aligned substantially perpendicularly to the surface of the medium, and on which information can be written along a track by perpendicular magnetization of the storage layer. The magnetic head further comprises a magnetic conductor body for carrying the magnetic flux having two pole legs which are arranged one behind the other in the direction of motion of the head and having a predetermined distance from each other, and with which at least one coil winding is associated, wherein, for performing the read function, the directions of the flux guidance in the two pole legs extend, at least substantially, antiparallel at their ends facing the recording medium. Such a magnetic head is known from DE-OS No. 29 24 013, corresponding to U.S. Pat. No. 4,287,544.
The principle of perpendicular magnetization for the storage of information is generally known. See, for instance, "IEEE Transactions on Magnetics", vol. MAG-16, No. 1, January 1980, pages 71 to 76, or the above-mentioned DE-OS No. 29 24 013. To utilize this principle, which is often also called vertical magnetization, special recording media are required such as a rigid magnetic storage disc, a flexible individual disc (floppy disc) or magnetic tape. Such a recording medium has at least one magnetizable storage layer of predetermined thickness, which contains a magnetically anisotropic material, particularly of a CoCr alloy, of which the axis of easy magnetization is perpendicular to the surface of the medium. By means of a separate write head, the individual bits of information are then written along a track in successive sections, also called cells or blocks, by magnetizing the storage layer. In practice, the magnetic flux reversals, i.e., the transitions from one direction of magnetization to the opposite one, are generally used as information bits. The sections have a predetermined extent in the longitudinal direction of the track, also called wavelength. This dimension can be substantially smaller as compared to the limit given in the method of longitudinal storage by demagnetization, so that the information density in the recording medium can advantageously be increased by the principle of vertical magnetization.
With this principle of vertical magnetization, however, problems arise in the development of suitable combined write/read heads, since, particularly, with these heads, the desired formation of the flux in a circuit with low magnetic resistance which is closed as far as possible, causes difficulties.
A suitable combined write/read head, i.e., a magnetic head, with which the write as well as read function can be performed, has in general, a so-called main pole by which a sufficiently strong vertical magnetic field is generated for the magnetic reversal of the individual sections in the storage layer. The necessary return for the flux can then be provided, for instance, by a so-called auxiliary pole on the opposite side of the recording medium. See the above cited literature reference "IEEE Trans. Magn.", vol. MAG-16. In addition, a return by leakage flux is also known See "IEEE Trans. Magn.", vol. MAG 18, No. 6, November 1982, pages 1170 to 1172.
A return can also be provided by a separate auxiliary pole which is located on the same side as the main pole. See "IEEE Trans. Magn.", vol. MAG-17, No. 6, November 1981, pages 3120 to 3122, vol. MAG-18, No. 6, November 1982, pages 1158 to 1163, or the DE-OS No. 29 24 013 mentioned above. Accordingly, the magnetic write and read head known from DE-OS No. 29 24 013 contains, on its forward end face, in the direction of motion of the recording medium moving away under it, an auxiliary pole and on its back side, the main pole proper. This main pole is formed by a pole leg which comprises substantially a thin pole piece which is arranged perpendicularly to the direction of motion and is applied to a nonmagnetic substrate. The auxiliary pole which is longer as seen in the direction of motion and which is located ahead of the main pole, forms a pole leg which is composed of several thin pole pieces arranged perpendicularly to the direction of motion with interposed insulating layers and which is separated from the main pole by an air gap. The extent of this air gap is relatively large and is, for instance, on the order of 5 to 10 .mu.m. An electrical winding is located in the air gap, by which the main pole is excited for the write function and, for the read function, the excitation of the main pole can be registered. The auxiliary pole serves in any case only for the return of the flux. Possible concurrent writing of the auxiliary pole can be tolerated since the writing main pole always follows it and thereby overwrites information that may have been written by the auxiliary pole, if the width of the auxiliary pole is not larger than that of the main pole, and thus, already written adjacent tracks remain uninfluenced. In addition, the larger cross section of the auxiliary pole as compared to the main pole and the relatively large extent of the air gap also are necessary in order to ensure a far-reaching reduction of the magnetic flux density at the auxiliary pole. Concurrent reading of the auxiliary pole, however, can lead to difficulties in the detection of the information.
The remaining space of the air gap which is not filled by the electrical winding and is facing the recording medium, must be filled with a so-called insulating gap layer. This gap layer should consist of a material as hard as possible such as Al.sub.2 O.sub.3 in order to avoid notching or washouts during the manufacture of the head, since such unevenesses can lead to a crash of the magnetic head which is guided over the recording medium with extremely little spacing, due to deposited dirt particles. It has been found, however, that the preparation of this gap layer disposed between the main and the auxiliary pole is extremely difficult.
Because of the mentioned difficulties in reading with the known combined read and write head, the functions of writing and reading can also be performed with separate heads so that then these heads can be optimally adapted to the respective function. See, for instance, "IEEE Trans. Magn.", vol. MAG16, No. 5, September 1980, pages 967 to 972. For reading, ring heads known per se can be used, while the writing must be carried out with special heads. Such a write head has, for instance, on its side facing the storage layer of the recording medium, a main pole, also called a single-pole head, with a longitudinal extent of, for instance, 3 .mu.m, opposite which a substantially larger auxiliary pole is arranged on the back side of the recording medium. The second head, required only for reading, is a known ring head and has a gap width of, for instance, 0.2 .mu.m. See "IEEE Trans. Magn." vol. MAG-17, No. 6, November 1981, pages 2538 to 2540. Such devices for reading and writing, with special heads adapted to the respective function, are relatively expensive from a mechanical design point of view, however.